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<br />1502
<br />
<br />During the 1971-72 water year, the Secre-
<br />tary of the Interior will be required to release
<br />9,055,000 acre-feet at Lee Ferry to meet the
<br />Colorado River Compact III (d) obligation
<br />of 75,000,000 acre-feet for the ten-year period
<br />1963-72.
<br />Because inflow to the Colorado River Ba-
<br />sin reservoirs was greater than outflow dur-
<br />ing 1970-71, storage in the system increased
<br />by 2,444,000 acre-feet. During the last three
<br />years, storage in the Basin has increased by
<br />8,771,000 acre-feet, or an average increase of
<br />2,923,000 acre-feet per year. Storage has in-
<br />creased because both Upper & Lower Basins
<br />have not completed planned developments.
<br />Tabl. 2
<br />CAPACITY, ACTIVE STORAGE, AND STORAGE CHANGE
<br />OF MAJOR COLORADO RIVER BASIN RESERVOIRS
<br />DURING WATER YEAR 1970-71
<br />(Thousands at Acre-F..t)
<br />
<br /> Active
<br /> Storagr Cb.lngr
<br /> Gross Usable Sepr. JO, During
<br />Up~r Basin C/lpacity Capacity /97/ Y""r
<br />Lake Powell .............. 27,000 25,002 13,609 +1,570
<br />Flaming Gorge '......... 3,789 3,749 2,911 +1,140
<br />Navajo ",............,,'.,., 1,709 1,696 993 -268
<br />Blue Mesa ,....,....,...,... 941 830 532 -278
<br />Fontenelle .'.'..'..'.'...... 345 345 327 +81
<br />Morrow Point ,........... 117 117 117 0
<br />Subtmal .........,.... JJ.901 31.739 18.509 +2.245
<br />Lowu Basin
<br />Lake Mead .................. 28,537 26,159 16.886 + 117
<br />Lake Mohave ............., 1.818 1,810 1,441 +65
<br />Lake Havasu .............. 648 619 574 +17
<br />Subtotal ,..",..,'.." 1l.OO3 28.588 18.901 +199
<br />Total Both Basins .'.' 64,904 60,327 37,410 +2,444
<br />
<br />Plate 4 shows the combined active surface
<br />storage and capacity of Lake Mead and the
<br />Colorado River Storage Project reservoirs for
<br />the period 1935-71. Lake Mohave and Lake
<br />Havasu are not included in Plate 4 because
<br />they are operated at relatively constant lev.
<br />els. The amount of water that percolated into
<br />the areas adjacent to Lake Powell and called
<br />"bank storage" continued to increase during
<br />197 L At the close of 1971, bank storage at
<br />Lake Powell was estimated to be 6.8 million
<br />acre-feet, or 48% of gross surface storage.
<br />
<br />Plate 5 shows the changes in storage of the
<br />major main stream reservoirs during 1970-
<br />7L
<br />
<br />PLATE 4
<br />
<br />COLORADO RIVER BASIN RESERVOIRS
<br />STOIlAGE ...NDCAP",CITT
<br />
<br />
<br />....-...
<br />".__.""n
<br />"'"'....
<br />',,"'''e'
<br />
<br />o
<br />,II. .000
<br />."U nu
<br />
<br />Water Uses in the United States
<br />
<br />Upper Basin. The depletion of the river
<br />above Lee Ferry is the result of inbasin con-
<br />sumptive use, transbasin diversions, and res-
<br />ervoir evaporation. The irrigated agriculture
<br />component of inbasin depletions, the largest
<br />of the three categories, is largely un-
<br />measured, but is estimated by applying unit
<br />water use factors to estimates of areas being
<br />irrigated. The preliminary total depletions in
<br />1970-71 above Lee Ferry were estimated by
<br />the Bureau of Reclamation to be 3,122,000
<br />acre-feet. This is an increase of 87,000 acre-
<br />feet over the estimated depletions for water
<br />year 1969-70. A breakdown of the 1970-71
<br />depletions is as follows: Acre-feet
<br />Inbasin Depletions .................,........................ 2,196,000
<br />Transbasin Diversions .................................. 450,000
<br />Reservoir Evaporation ................................., 476,000
<br />
<br />Total ...............,...,............',............................ 3,122,000
<br />
<br />Lower Basin. Diversions minus meas-
<br />ured return flows to the river by the major
<br />Lower Basin mainstream users in 1970-71
<br />were 6,260,000 acre-feet. This is an increase
<br />of 390,000 acre-feet over the use in 1969-70.
<br />California's diversions less return flows to
<br />the river were 5,100,000 acre-feet. This is an
<br />increase of 264,000 acre-feet over the diver-
<br />sions less returns for 1969-70.
<br />Lower Basin water use from the river for
<br />the last five years is shown in Table 3.
<br />
<br />15
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